Method and apparatus for high-performance bonding resequencing

ABSTRACT

A method, system, and computer program product for receiving and resequencing a plurality of data segments received on a plurality of channels of a bonding channel set, comprising deter mining if a sequence number of a received segment matches an expected sequence number. If so, the process includes forwarding the segment for further processing, incrementing the expected sequence number; and forwarding any queued packets corresponding to the expected sequence number and immediately succeeding sequence numbers less than a sequence number of annexed missing segment. If the sequence number of the received segment does not match the expected sequence number, the received segment is queued at a memory location. The address of this location is converted to a segment index. The segment index is stored in a sparse array.

This application is a continuation of U.S. application Ser. No.11/902,603, filed Sep. 24, 2007, now U.S. Pat. No. 7,751,404, whichclaims the benefit of U.S. Provisional Application No. 60/849,836, filedon Oct. 6, 2006, all of which are incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention described herein relates to communications systems, andmore particularly relates to transmission and processing of segmented orpacketized data.

2. Related Art

Channel bonding is the process of taking multiple independentcommunications channels between two points and treating them as thoughthey were a single “virtual” channel with more total bandwidth thanwould otherwise be possible. In addition to greater capacity, thisarrangement has additional benefits such as increased overallreliability of a virtual channel. Given that a virtual channel is madeof multiple physical channels, there is inherent redundancy that allowsfor continued operation if one or more physical channels fail.

The concept of channel bonding is illustrated generally in the cablecommunications system of FIG. 1. In this example, a cable modemtermination system (CMTS) 110 is shown in communication with a cablemodem (CM) 130. Data passes from CMTS 110, via channels 120 a through120 i, to CM 130. During a given session, some or all of channels 120 athough 120 i can be bonded together, so that segmented data for thesession (e.g., packets) can be sent through these channels. A givensegment or packet will be sent over one of the channels; the nextsegment or packet may be sent over the same channel, or over a differentchannel in this bonding channel set (BCS). The CM 130 must thenreassemble the segments or packets in order before delivery to an enduser.

One approach for sending data on the bonded channels is for the sendingend to transmit entire packets, spreading them out among the channelsbased on load balancing, rate limiting, or other means for selectingchannels. Another approach is to concatenate a series of packets into abyte stream, subdividing the stream into segments for transmission onvarious channels. In either case, the packets/segments are tagged with asequence number by the transmitting entity (e.g., the CMTS) so that thereceiving entity (e.g., the CM) can reproduce the data stream in theproper packet/segment order. This is known as resequencing, and ensuresthat data is not delivered out of order to the end user.

Resequencing across multiple bonded channels, however, can be atime-intensive process and may consume considerable memory. Segments orpackets may be received out of order. At the receiving end, gaps mayappear, where a segment or packet goes missing while one or more laternumbered segments are received on any of the several bonded channels.Such later numbered segments must be saved in memory until the missingsegment is received. At this point the missing segment can be deliveredto the end user, along with any saved segments that sequentially followthe missing segment. Such saved segments must be read from memory anddelivered to the user in numerical order.

A high-performance, low-cost device like a cable modem can benefit froman efficient method for queuing packets for resequencing. Ideally, animplementation in a CM or CMTS would be fast and not require largeamounts of memory/register resources. What is needed, therefore, is asystem and method for efficiently resequencing packets or other datasegments at a receiving node, wherein the resequencing process requiresminimal memory and operates relatively rapidly.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram illustrating a set of bonded channels in acommunications system.

FIG. 2 is a flowchart illustrating the processing of an embodiment ofthe invention.

FIG. 3 is a flowchart illustrating the process of queuing a segment,according to an embodiment of the invention.

FIG. 4 is a flowchart illustrating the process of determining whether asegment is lost, according to an embodiment of the invention.

FIG. 5 is a flowchart illustrating the process of removing a segmentfrom a queue, according to an embodiment of the invention.

FIGS. 6-9 illustrate the structure and content of an exemplary sparsearray at various stages of processing, according to an embodiment of theinvention.

FIG. 10 is a block diagram illustrating the computing environment of theinvention, according to an embodiment thereof

Further embodiments, features, and advantages of the present invention,as well as the operation of the various embodiments of the presentinvention, are described below with reference to the accompanyingdrawings.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention is now described withreference to the figures, where like reference numbers indicateidentical or functionally similar elements. Also in the figures, theleftmost digit of each reference number corresponds to the figure inwhich the reference number is first used. While specific configurationsand arrangements are discussed, it should be understood that this isdone for illustrative purposes only. A person skilled in the relevantart will recognize that other configurations and arrangements can beused without departing from the spirit and scope of the invention. Itwill be apparent to a person skilled in the relevant art that thisinvention can also be employed in a variety of other systems andapplications.

I. Introduction

The invention described herein represents a method and system forresequencing packets or segmented data that is received through a BCS.Given that the segments may be received out of order, the inventionresequences the segments at the receive end for delivery to an end user.Some segments may be lost and never received. The invention allows thereceive end to determine whether a missing segment should be consideredlost, and to continue processing segments. The invention may be embodiedin software or hardware, or a combination of both.

The system can be applied to communications conforming to a version ofthe

Data Over Cable System Interface Specification (DOCSIS) standard, or asimilar standard. For example, the invention may be implemented in acable modem or other end user device that receives downstream datasegments or packets from a cable modem termination system over a set ofbonded channels. The following discussion is therefore presented interms of downstream communications from a CMTS to a CM. Note howeverthat the invention may also be applied with respect to bonded channelupstream communications, from a CM to a CMTS. Moreover, the inventionmay also be applied to DOCSIS based systems that use a medium other thancable, including but not limited to fiber and wireless media. Theinvention may also be applied in communications systems that do notconform to any version of a DOCSIS standard.

II. Terminology

The following terms are used to describe bonding operations. Some of theterms are also defined by the DOCSIS 3.0 specification:

RCS: Receive channel set. This is the set of communications channels onwhich the receiving entity is capable of receiving data.

BCS: Bonding channel set. This is a subset of the RCS and represents thechannels that the transmitting and receiving entities have agreed to usefor sending data associated with a bonding session.

Bonding session: The state information used by the transmitting andreceiving entities for performing bonding. There can be multiple bondingsessions active at the same time.

DSID: Downstream service identifier. This is used to identify aparticular downstream bonding session (upstream bonding uses a differentmechanism to identify the session). Downstream segments or packets canbe tagged with the DSID so that the CM knows to which session the packetor segment belongs.

PSN: Packet sequence number. This is a number indicating the order of asegment or packet in a bonding session relative to other segments orpackets in the bonding session. Packets or segments are tagged with thePSN so that the receiving entity knows how to resequence them. Note thatDOCSIS 3.0 requires packets to be sent in increasing PSN order on achannel (e.g., the transmitting entity can send PSN 3 then PSN 5 onchannel 0, but it cannot send PSN 5 followed by PSN 3).

Channel ID: A number representing the channel on which a segment orpacket was received. Packets or segments are not tagged with the channelID, since the receiving channel is necessarily known by the receivingentity.

This invention is applicable to any bonded channel communications systemthat transmits and processes individual blocks of data that result fromthe segmentation of a larger data stream. Such segments may or may notbe packets, as this term is conventionally understood by a person ofordinary skill in the art. The term “segment” will therefore be usedthroughout the remainder of this discussion.

III. Resequencing

The receiving entity, e.g., a CM, maintains a counter or variablerepresenting the

PSN of the next expected segment in any given bonding session. Areceived segment will be tagged with a PSN and a DSID identifying thebonding session. When the CM receives a segment, the CM looks up thebonding session associated with the DSID of the segment. If the PSN ofthe segment matches the PSN that is expected next for the session, thesegment is forwarded and the session's state is updated by incrementingthe next expected PSN. If the PSN does not match the next expected PSN,the segment is queued for later processing, based on the assumption thatthe segment having the next expected PSN should arrive on one of the BCSchannels at some point in the future. In this case the next expected PSNis not incremented.

Segments with higher PSNs may arrive before segments with lower PSNs fora number of reasons. Some examples include:

-   -   Channel congestion—The CMTS queues a segment identified by PSN 1        to be sent on channel 0, and queues a segment identified by PSN        2 on channel 1. However, if some other segment was previously        queued to be sent on channel 0, then the segment identified by        PSN 1 must wait and may be sent later than the segment        identified by PSN 2. The segment of PSN 2 may therefore arrive        before the segment of PSN 1.    -   Latency/speed—If the channels in the BCS have different        characteristics (interleaver depth, modulation rate, etc.), then        segments queued to be sent at the same time will arrive at        different times simply because it takes longer for the bits to        traverse a “slower” channel.    -   Segment size—A segment can only be processed by the CM when all        of the bits have arrived. All other things being equal, a        smaller segment may therefore be treated as having arrived        sooner than a larger segment.    -   Channel service ordering—The CM can receive segments        simultaneously on multiple channels, but may service the        channels in an order that causes segments to be processed in        non-PSN order.    -   Segment loss—A segment with a lower PSN might be lost (due to        error, overflow, etc), causing segments with higher PSNs to be        queued until a timeout expires or some other event takes place        that forces the CM to treat the missing segment(s) as        unrecoverable. This is discussed in greater detail below.    -   More than one of these situations may be present at the same        time.

The CM must buffer segments with higher PSNs until the missing segmentsarrive. If the missing segments are lost, either a timeout or rapid lossdetection will cause the missing segments to be skipped and treated asunrecoverable.

An embodiment of the resequencing process is illustrated in FIG. 2. FIG.2 illustrates a process for receiving of a segment and either saving thesegment or forwarding the segment, as necessary. The process starts atstep 205. In step 210, the segment is received by a receiving entity,such as a CM. In step 215, the DSID and the PSN of the segment are read.In step 220, the receiving entity looks up the bonding session of thesegment, as indicated by the DSID. In step 225, a determination is madeas to whether the received PSN matches the value representing the nextexpected PSN for this session.

If so, then in step 240, the received segment is forwarded on to the enduser. The segment may alternatively be forwarded for additionalprocessing. In step 245, the value indicating the next expected PSN isincremented. In step 250, a determination is made as to whether there isa queued segment corresponding to the incremented expected PSN. If not,the process returns to step 210, where the next segment is received. Ifit is determined in step 250 that there is a queued segmentcorresponding to the expected PSN, then the process continues at step240, where the queued segment is forwarded.

If, in step 225, the PSN of the received segment is greater than theexpected PSN for the session, then in step 230 the segment is queued.Step 230 will be discussed in greater detail below with respect to FIG.3.

In step 235, a determination is made as to whether there are anyunreceived segments that should be treated as lost. This step will bediscussed in greater detail below with respect to FIG. 4. The processthen returns to step 210.

FIG. 3 illustrates in greater detail step 230, the queuing of a receivedsegment. The process begins at step 310. In step 320, the receivedsegment is written to a buffer. In step 330, the buffer address isconverted into a segment index. In step 340, the PSN of the receivedsegment is hashed to generate a sparse array index. In step 350, thesegment index is written to the sparse array at the location indicatedby the sparse array index derived above in step 340. In step 360, theprocess concludes.

Step 235, the determination of whether any previous unreceived segmentshave been lost, is illustrated in greater detail in FIG. 4 according toan embodiment of the invention. The process as illustrated begins atstep 410, then applies two tests to determine if a segment should betreated as lost. In step 420, the first test is applied: a determinationis made as to whether a queued segment is present on each channel of theBCS. If so, the process continues at step 440. Here, the value of theexpected PSN is advanced to the PSN corresponding to the next segmentthat has been received. Therefore, when enough segments have been queued(as determined by the presence of one or more queued segments on eachchannel), it is determined that the volume of waiting (i.e., queued)data is sufficient to merit the designation of any unreceived packet(s)as lost. This allows the expected PSN to be incremented to the PSN ofthe next received segment (step 440). This queued segment is thenforwarded (step 445). Step 445 includes the removal of such segmentsfrom a queue; this operation is discussed in greater detail below withrespect to FIG. 5.

If, in step 420, the determination is made that not every channel of theBCS has a queued segment, then the process continues at step 430. Here,the second test is applied: a determination is made as to whether agiven unreceived segment has been missing for longer than apredetermined period. If not, the process concludes at step 450. But ifa missing segment has been missing for longer than the predeterminedperiod, then the missing segment is said to have timed out. The processhas waited long enough, as defined by the predetermined period, to merittreating the unreceived segment as lost. The expected PSN is thenincremented in step 460, skipping over the missing segment.

If it is determined in step 470 that the expected PSN now indicates asegment that is currently queued, then the queued segment is forwardedin step 480. The process then continues at step 460, where the expectedPSN is incremented again. The cycle of incrementing the expected PSN(step 460) and forwarding the indicated segment (step 480) continues aslong as a queued segment corresponding to the expected PSN remains, asdetermined in step 470.

If, in step 470, it is determined that there is no queued segmentcorresponding to the expected PSN, then the process returns to step 430,where it is determined if any additional missing segment has timed out.

Note that steps 420 and 430 represent two conditions, either of whichsignify that one or more missing segments are to be treated as lost. Inalternative embodiments of the invention, other tests may be used inlieu of, or in addition to, these tests.

FIG. 5 illustrates a process for removing a segment from a queue,according to an embodiment of the invention. The process begins at step510. In step 520, the PSN of the queued segment is hashed to generate anindex to a sparse array. In step 530, a segment index is read from thesparse array. In particular, the segment index is read from the locationin the sparse array indicated by the sparse array index generated above.In step 540, the segment index is converted into a buffer address. Instep 550, the segment is read from memory at the buffer address. Theprocess concludes at step 560.

The steps in the process discussed above are illustrated further withthe following example. Note that while the following discussiondescribes the processing of the invention in terms of downstreamcommunications over a bonded channel set from a CMTS to a CM, theprocess can be applied in an upstream direction as well. Moreover, theinvention is not limited to cable media or to DOCSIS-relatedcommunications.

IV. Example

The following illustrates the operation of an embodiment of theinvention. This example is presented for purposes of showing how theinvention functions in the context of a hypothetical BCS that is used totransmit a set of data segments. This is an example only, and is notintended to limit the scope of the invention.

Assume that a CM has an RCS of four channels (channels 0-3). Assumefurther that there is a single bonding session with DSID 1, and that theBCS of the session consists of three channels (0-2). The CM is waitingfor the next segment, with the expected PSN having a value of 10 on DSID1. The table below shows the PSNs of segments that were sent by theCMTS. The table also shows when the segments were sent and the channelson which they were sent. Blank entries indicate that no segments weresent at a particular time and channel. In this example, segments withPSN 10, 15, 17, and 19 are missing, perhaps due to errors on thechannel.

Channel Time 0 1 2 3 7 6 5

4 20 18 3 16

2 14

12 1 13 11 0

The following events take place:

At time 0: The segment having PSN 10 is sent by the CMTS but nothing isreceived at the CM.

At time 1:

-   -   The segment having PSN 13 arrives on channel 0. This does not        match the expected next PSN of 10, so this received segment is        queued for later processing.    -   The segment having PSN 11 arrives on channel 1. This does not        match the expected next PSN of 10 and is queued.

At time 2:

-   -   The segment having PSN 14 arrives on channel 0. This does not        match the expected next PSN of 10 and is queued.    -   The segment having PSN 15 is sent by the CMTS but not received        at the CM.    -   The segment having PSN 12 arrives on channel 2. This does not        match the expected next PSN of 10 and is queued.    -   The CM now has a segment queued on each channel of the BCS, so        it can assume that PSN 10 was lost. Segments with PSN 11, 12,        13, and 14 can be forwarded immediately.    -   The next expected PSN is set to 15, and the CM has no segments        queued on any channel.

At time 3:

-   -   The segment having PSN 16 arrives on channel 1. This does not        match the expected next PSN of 15 and is queued.    -   The segment having PSN 17 is sent by the CMTS but not received        at the CM.

At time 4:

-   -   The segment having PSN 20 wives on channel 1. This does not        match the expected next PSN of 15 and is queued.    -   The segment having PSN 18 arrives on channel 2. This does not        match the expected next PSN of 15 and is queued.

At time 5:

-   -   The segment having PSN 19 is sent by the CMTS but not received        at the CM.

At future time N (where N represents the end of the timeout period):

-   -   The CM times out waiting for the segment having PSN 15, and        assumes that this segment was lost.    -   The segment with PSN 16 can be forwarded immediately.    -   The next expected PSN is set to 17.

At future time N+1:

-   -   The CM times out waiting for the segment having PSN 17, and        assumes that this segment was lost.    -   The segment with PSN 18 is forwarded immediately.    -   The next expected PSN is set to 19.

At future time N+3:

-   -   The CM times out waiting for the segment having PSN 19, and        assumes that this segment was lost.    -   The segment with PSN 20 can be forwarded immediately.    -   The next expected PSN is set to 21.

V. Implementation of an Embodiment of the Invention

As discussed above, a CM is required to keep track of the per-bondingsession state, particularly the next expected PSN, and provide storagefor queuing segments that have a PSN not matching the next expected PSN.It must also keep track of timers and/or timestamps associated withsegments that are missing. This can be used in timeout processing,described below, when determining whether missing segments areunrecoverable.

The segment queues and timers/timestamps can consume a substantialamount of memory depending on what mechanism is used to represent them.This increases system cost (requiring larger memories to track thestate), and decreases system efficiency since the large amount of datamust be accessed frequently (causing lots of bus/RAM accesses andthrashing the cache).

The number of segments and timers/timestamps needed to avoid segmentloss due to local system resources can be calculated based on thebonding channel characteristics. The maximum number of segments that mayhave to be queued, NumEntries, can be estimated as follows:NumEntries=PacketRate*(MaxDelayMs/1000)*NumChannelswhere

-   PacketRate is the number of segments received per second per    channel,-   MaxDelayMs is the maximum delay for any segment, measured in    milliseconds,    and-   NumChannels is the number of channels in the BCS.-   Note that in the case where the channels are not loaded    symmetrically, the equation becomes:    NumEntries=AggregatePacketRate*(MaxDelayMs/1000)    where AggregatePacketRate is the rate at which segments are received    across all channels of the BCS, as measured in segments per second.    Thus, if the expected packet rate is 88 k segments per second per    channel, the maximum channel delay is 23 ms, and there are 4    channels:    NumEntries=88,000*(23/1000)*4=8096 entries per bonding session.

If a standard doubly linked list is used (assuming 12 bytes per entry),this consumes almost 95 k bytes of memory per bonding session. If a CMis required to support at least 16 sessions, this would consumeapproximately 1.5 MB of RAM.

Poor segment queue organization can lead to even worse CM forwardingperformance, because segments must be forwarded in PSN order, but arefrequently not received in PSN order. The CM needs to manage the queuefrequently (add/remove/find segments and timers/timestamps), and thequeue organization affects the number of operations performed.

A method for storing segments and timestamps for resequencing is to usea sparse array (also known as a vector). For a given segment, the arrayis accessed by using a hash of the PSN of the segment. In an embodimentof the invention, the sparse array is an array of 16-bit values. Thismay be chosen because it can be a natural size for a CPU, and it allowsthe CM to keep track of a large number of outstanding segments forresequencing while limiting the amount of memory that is used. Otherembodiments can use values of 32 bits or more.

If the bonding channel characteristics (e.g., PacketRate, MaxDelayMs,and NumChannels) suggest that fewer entries are needed to storesegments, then the array values could be of a different size (e.g. 8bits). If there are more channels, then larger entries may be required(e.g. 32 bits). A hardware implementation could alternatively use anarbitrary bit size (e.g. 12 bits), tailored to match an alternativehardware environment.

If the PSN is a 16-bit value, this means that a direct-mapped sparsearray would have 64 k entries; if an entry is 16 bits long, this willconsume 128 k bytes. This can be inefficient, though, since only enoughsegments are needed to satisfy the MaxDelayMs value (almost 8 k entriesin the previous example). As a result, the size of the sparse array maybe smaller than 64 k entries.

Note that in a software implementation, it may be convenient to make thesparse array size a power of two. This is so that the sparse array indexand the PSN wrap back to zero uniformly with each other, making trackingthe current offset easier. A hardware implementation (or a more complexsoftware implementation) could allow the sparse array size to be otherthan a power of two.

The NumEntries value calculated by the equation above can be rounded upor down as desired in order to make it a power of two (rounding downuses less memory but runs the risk of not being able to buffer enoughsegments; rounding up uses more memory, but guarantees that segmentswill not be discarded due to buffering constraints at high segmentrates). High segment rates may be unlikely except in limited stresstests, in which case rounding down would be acceptable.

FIG. 6 following shows the state of a sparse array based on the previousresequencing example. The sparse array has M entries. Note that in theillustrated embodiment, 0xffff is a special value that indicates “slotempty”—a segment is not queued, and a timeout is not active. If themillisecond clock count is 0x7fff (which would cause 0xffff to bestored), then the clock count is incremented to 0x0000, and 0x8000 isstored. This will cause segments to be buffered 1 ms longer than the maxtimeout, but such a discrepancy is allowed by the DOCSIS specification.

The entries in the sparse array are indexed by the PSN associated withthe segment. In an embodiment of the invention, the hash is simply thePSN reduced by a modulus equal to the array size:

-   SparseArrayIndex=PSN mod ArraySize

Thus, if the array size is 4096, then the array indices for PSNs 1,4098, and 7121 are as follows:

-   SparseArrayIndex=1 mod 4096=1-   SparseArrayIndex=4098 mod 4096=2-   SparseArrayIndex=7121 mod 4096=3025

The segment index N is stored in a sparse array entry, and is calculatedfrom the segment buffer address; when a segment is received on thedownstream, it can be stored through direct memory access (DMA) into abuffer. The buffer is tracked via a 32-bit address in this example. Thisaddress is too large to store in the 15-bit field available in thesparse array entry. However, since the DMA buffers are contiguous inmemory, and are of a uniform size, a segment index can be calculatedfrom the buffer address at which the segment is stored:SegmentIndex=(BufferAddress−BaseAddress)/BufferSize

For example, if the BaseAddress for the DMA buffers is 0x80201380, andeach buffer is 2048 bytes, then the packet indices for buffers withaddresses 0x80205b80 and 0x80226b80 are:SegmentIndex=(0x80205b80−0x80201380)/2048=9SegmentIndex=(0x80226b80−0x80201380)/2048=75Likewise, a pointer can be calculated from its index:BufferAddress=(SegmentIndex*BufferSize)+BaseAddress

Using the same buffers from the previous example:BufferAddress=(9*2048)+0x80201380=0x80205b80BufferAddress=(75*2048)+0x80201380=0x80226b80

As noted previously, when a segment arrives on the downstream, if thePSN does not match the next expected PSN for the bonding session, thenthe CM can buffer the segment and start a timeout timer for the missingsegment(s).

The CM converts the address of the buffer into a segment index, andhashes the

PSN to find the entry in the sparse array to store the segment index.Then, for each entry from the next expected PSN to the PSN of thesegment that was received, the CM calculates the current millisecondtime (modulus 15 bits, with the MSB set to 1), and stores this clockcount to indicate the time when the gap was formed. The clock count canbe viewed as a timeout value.

For example, if the next expected PSN is 10, a segment with PSN 13arrives at time 40, and is stored via DMA into the buffer with address0x80226b80 (segment index 75), then the sparse array will be as shown inFIG. 7.

Later, if one of the missing segments arrives (which has a timeout valuein the sparse array), the segment index overwrites the timeout value,effectively canceling the timeout for that entry. For example, if asegment with PSN 11 arrives at time 41 and is stored into the bufferwith address 0x80205b80 (segment index 9), then the sparse array will beas shown in FIG. 8.

If segments with PSNs 10 and 12 never arrive (e.g., lost due to errors,etc.), then the queued segments will be released from the queue once theMaxDelayMs time has elapsed. Once a timeout expires or a segment isforwarded from the queue, the value for that entry is set to 0xffff toindicate that the slot is not being used. This is shown in FIG. 9.

Note that the mapping of timer values and segment indices to a 15-bitvalue (with another bit used to signify whether the other 15 bitsrepresent a timer value or a segment index) is exemplary only. Thisparticular arrangement is not meant to limit the scope of the invention.Alternative embodiments are also feasible, as would be known to a personof skill in the art.

VI. Computing Context

In an embodiment of the present invention, the processing of theinvention described herein is implemented using control logic (software)that is executed in one or more computer systems, such as computersystem 1000 shown in FIG. 10. The computer system 1000 can be anycomputer system capable of performing the functions described herein. Inan embodiment of the invention, such a computer system is incorporatedin a communications device, such as CM 130, or such as CMTS 110.

The computer system 1000 includes one or more processors (also calledcentral processing units, or CPUs), such as a processor 1004. Theprocessor 1004 is connected to a communication bus 1006. The computersystem 1000 also includes a memory 1008, such as random access memory(RAM). The main memory 1008 has stored therein control logic (computersoftware), and data.

The computer system 1000 may also include one or more secondary storagedevices 1010. The secondary storage devices 1010 may include, forexample, a hard disk drive 1012 and/or a removable storage device ordrive 1014. The removable storage drive 1014 can represent a compactdisk drive, an optical storage device, etc.

The removable storage drive 1014 interacts with a removable storage unit1018. The removable storage unit 1018 includes a computer useable orreadable storage medium having stored therein computer software (controllogic) and/or data. Removable storage unit 1018 can represent an opticalstorage disk, flash memory device, or any other computer data storagedevice. The removable storage drive 1014 reads from and/or writes to theremovable storage unit 1018 in a well known manner.

The computer system 1000 further includes a communication or networkinterface 1024. The communications interface 1024 enables the computersystem 1000 to communicate with remote devices. For example, thecommunications interface 1024 allows the computer system 1000 tocommunicate over a communication network or path 1026. The networkinterface 1024 may interface via wired or wireless connections.

Control logic may be transmitted to and from the computer system 1000via the communication path 1026. More particularly, the computer system1000 may receive and transmit carrier waves (electromagnetic signals)modulated with control logic via the communications path 1026.

Any apparatus or manufacture comprising a computer useable or readablemedium having control logic (software) stored therein is referred toherein as a computer program product or program storage device. Thisincludes, but is not limited to, the computer system 1000, the mainmemory 1008, the hard disk 1012, and/or the removable storage units1018. Such computer program products, having control logic storedtherein that, when executed by one or more data processing devices,cause such data processing devices to operate as described herein,represent embodiments of the invention. In particular, the functionalitydescribed above, such as that illustrated in FIGS. 2-5 and theaccompanying text and examples, can be embodied as one or more computerprogram products.

The invention can work with software, hardware, and/or operating systemimplementations other than those described herein. Any software,hardware, and operating system implementations suitable for performingthe functions described herein can be used.

VII. Conclusion

The above discussion shows the following attributes of this invention:

Adding and removing entries in the queue comprises reading and writing asingle value (e.g., 16-bits). There is no need to manage node pointersas in a traditional linked list.

Finding the location where a segment should be stored includes hashingthe PSN, rather than searching through a list of segments alreadyqueued.

Forwarding segments in PSN order includes incrementing an index value(next PSN), rather than walking linked lists.

Timeouts/timers are managed via the same mechanism as segments, anddon't require separate memory or state.

The CM can check to see if a timer has expired by using subtraction(CurrentTimeMs−SparseArray[Next PSN]>=MaxDelayMs).

While some embodiments of the present invention have been describedabove, it should be understood that it has been presented by way ofexamples only and not meant to limit the invention. It will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined in the appended claims. Thus, the breadthand scope of the present invention should not be limited by theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method for determining whether an expected segment from a bondingsession is lost, comprising: (a) receiving a segment over a bondingchannel from among a bonding channel set (BCS); (b) determining if asequence number of the segment matches an expected sequence number of anexpected segment; (c) queuing the segment when the sequence number doesnot match the expected sequence number; and (d) designating the expectedsegment as lost when there is at least one queued segment thatcorresponds to each bonding channel of the BCS.
 2. The method of claim1, further comprising: (e) forwarding the segment for further processingwhen the sequence number matches the expected sequence number.
 3. Themethod of claim 2, wherein step (e) comprises: (e)(i) forwarding thesegment and any queue segments that correspond to succeeding sequencenumbers less than a sequence number of the expected sequence number forfurther processing.
 4. The method of claim 1, wherein step (c)comprises: (c)(i) queuing the segment in a memory at a location whoseaddress is converted to a segment index.
 5. The method of claim 4,wherein step (c)(i) comprises: (c)(i)(A) writing the segment to a bufferin the memory; (c)(i)(B) converting the address of the buffer into thesegment index; (c)(i)(C) hashing the sequence number of the segment tocreate an index to a sparse array; and (c)(i)(D) writing the segmentindex to the sparse array at a location in the sparse array indicated bythe index to sparse array.
 6. The method of claim 1, further comprising:(e) determining if any missing segment has been missing for longer thana predetermined interval; and (f) designating the missing segment aslost when the missing segment has been missing for longer than apredetermined interval.
 7. The method of claim 1, further comprising:(e) incrementing the expected sequence number to a sequence number of anext segment.
 8. A cable modem configured to receive a segment over abonding channel from among a bonding channel set (BCS), comprising: aprocessor configured to determine if a sequence number of the segmentmatches an expected sequence number of an expected segment; and a memoryconfigured to queue the segment when the sequence number does not matchthe expected sequence number, wherein the processor is configured todesignate the expected segment as lost when there is at least one queuedsegment that corresponds to each bonding channel of the BCS.
 9. Thecable modem of claim 8, wherein the processor is further configured toforward the segment for further processing when the sequence numbermatches the expected sequence number.
 10. The cable modem of claim 9,wherein the processor is further configured to forward any queuesegments that correspond to succeeding sequence numbers less than asequence number of the expected sequence number for further processing.11. The cable modem of claim 8, wherein the memory is configured toqueue the segment at a location whose address is converted to a segmentindex.
 12. The cable modem of claim 11, wherein the memory is configuredand arranged to form a sparse array, the memory being configured toqueue the segment by: (i) writing the segment to a buffer; (ii)converting the address of the buffer into the segment index; (iii)hashing the sequence number of the segment to create an index to thesparse array; and (iv) writing the segment index to the sparse array ata location in the sparse array indicated by the index to sparse array.13. The cable modem of claim 8, wherein the processor is furtherconfigured to determine if any missing segment has been missing forlonger than a predetermined interval and to designate the missingsegment as lost when the missing segment has been missing for longerthan a predetermined interval.
 14. The cable modem of claim 8, whereinthe processor is further configured to increment the expected sequencenumber to a sequence number of a next segment.
 15. A cable modemtermination system configured to receive a segment over a bondingchannel from among a bonding channel set (BCS), comprising: a processorconfigured to determine if a sequence number of the segment matches anexpected sequence number of an expected segment; and a memory configuredto queue the segment when the sequence number does not match theexpected sequence number, wherein the processor is configured todesignate the expected segment as lost when there is at least one queuedsegment that corresponds to each bonding channel of the BCS.
 16. Thecable modem termination system of claim 15, wherein the processor isfurther configured to forward the segment for further processing whenthe sequence number matches the expected sequence number.
 17. The cablemodem termination system of claim 16, wherein the processor is furtherconfigured to forward any queue segments that correspond to succeedingsequence numbers less than a sequence number of the expected sequencenumber for further processing.
 18. The cable modem termination system ofclaim 15, wherein the memory is configured to queue the segment at alocation whose address is converted to a segment index.
 19. The cablemodem termination system of claim 18, wherein the memory is configuredand arranged to form a sparse array, the memory being configured toqueue the segment by: (i) writing the segment to a buffer; (ii)converting the address of the buffer into the segment index; (iii)hashing the sequence number of the segment to create an index to thesparse array; and (iv) writing the segment index to the sparse array ata location in the sparse array indicated by the index to sparse array.20. The cable modem termination system of claim 15, wherein theprocessor is further configured to determine if any missing segment hasbeen missing for longer than a predetermined interval and to designatethe missing segment as lost when the missing segment has been missingfor longer than a predetermined interval.